Methadone maintenance clients who continue substantial use of heroin present a problem to treatment personnel. For these clients, standard maintenance treatment has not served to sufficiently reduce heroin use, and there is no generally accepted, specific treatment for these people. The objective of this research is to assess the effectiveness of an increase in methadone dose in reducing the heroin use of the subgroup of clients. Subject are clients at two different methadone maintenance programs. Subjects in the dose increment group have their doses increased by amounts of 100% to 50%, depending on starting dose. Subjects in the dose stabilization group receive standard treatment but not methadone dose changes. Subjects will participate in the study for 14 weeks. Subjects in both groups complete two brief questionnaires on mood states and dose-related symptoms once a week. A total of 40 subjects will be recruited. Dependent veriables are number of opiate-positive specimens, attrition from the experiment, and termination from treatment. Treatment group differences in outcome will be examined by analysis of variance techniques.